1. Field of the Invention
The present invention relates to a current drive apparatus, a drive method of the current drive apparatus, and a display apparatus using the current drive apparatus, and more particularly to a current drive apparatus including a structure to operate a plurality of loads by applying a predetermined current thereto, a drive method thereof, and a display apparatus which displays desired image information in a display panel by using the current drive apparatus.
2. Description of the Related Art
Conventionally, there is known a light emitting element type display including a display panel in which a plurality of organic electroluminescence elements (which will be referred to as “organic EL elements” hereinafter), inorganic electroluminescence elements (which will be referred to as “inorganic EL elements” hereinafter), or self-luminous type light emitting elements (optical elements) such as light emitting diodes are arranged in a matrix form.
As compared with a liquid crystal display (LCD) which has considerably spread in recent years, such a light emitting element type display has a higher display response speed and no field angle dependency, an increase in contrast, realization of high definition of a display image quality and a reduction in power consumption are possible. Further, a reduction in thickness and weight of one layer is possible since it does not require a back light as different from the liquid crystal display. Thus, it has a very excellent characteristic, so that the light emitting element type display has been studied and developed vigorously as a display of the next generation.
Such a display generally includes a display panel in which display pixels including light emitting elements are arranged in the vicinity of respective intersects of scanning lines arranged in a row direction and data lines arranged in a column direction, a data driver which generates a predetermined drive current according to display data and supplies it to each display element through the data lines, and a scanning driver which causes display pixels in a predetermined row to enter a selection state by applying a scanning signal with a predetermined timing. In such an apparatus, by causing each light emitting element to perform the light emitting operation with a predetermined brightness gradation according to the display data by using the drive current supplied to each display pixel, desired image information is displayed in the display panel. A concrete example of the light emitting element type display will be described in detail in conjunction with a later-described embodiment.
Here, in the display drive operation in the display, there are known a current specification type drive mode which sequentially repeats in accordance with each row for one screen the operation which generates drive currents having individual current values according to the display data with respect to a plurality of display pixels, simultaneously supplies the currents to the display pixels in a specific row and causes the light emitting element of each display pixel to emits the light with a predetermined brightness gradation, and a pulse width modulation (PWM) type drive mode which sequentially repeats for one screen the operation which supplies drive currents having a fixed current value with individual time widths (signal widths) according to the display data relative to a plurality of the display pixels to the display pixels in a specific row in the same display period and causes each light emitting element to emit the light with a predetermined brightness gradation.
In these display drive operations, the drive currents having predetermined current values or a fixed current value according to the display data must be supplied to a plurality of the display pixels in each row at the same time or within the same display period. In order to cope with realization of high definition and a large screen of a thin display device in recent years, there is known a display having applied thereto a circuit configuration which includes a plurality of driver chips (semiconductor chips) each having a predetermined number of output terminals as the above-described data drivers, individually generates the drive currents in the respective driver chips and supplies the drive currents to the respective light emitting elements through a data line at the same time.
The display to which the above-described data driver including a plurality of the driver chips is applied has the following problems.
The conventional data driver having a plurality of the driver chips includes a circuit used to individually generate a drive current in accordance with each driver chip and has a structure to simultaneously supply the drive currents to the respective light emitting elements from the respective driver chips through respective output terminals. Therefore, when irregularities are generated in current values of the drive currents outputted from a plurality of the driver chips, irregularities occur in the light emitting state in each display pixel (brightness gradation of the light emitting element), and the display heterogeneity is produced. Thus, irregularities in the drive currents must be suppressed as much as possible between the respective driver chips and between the respective output terminals.
However, in the field of a semiconductor manufacture technique, there is known the fact that irregularities are necessarily generated in the element characteristic of function elements such as transistor elements, resistance elements or capacitance elements formed on the same semiconductor chip. Such irregularities in the element characteristic can be suppressed to some degree by, e.g., optimizing manufacturing processes, but they cannot be completely eliminated. Further, there has been reported the fact that irregularities in the number of impurity atoms in channels become relatively actual with a reduction in design minimum dimension applied to the transistor elements and irregularities are thereby generated in a threshold value or the mobility.
Therefore, there is a problem that it is very difficult to greatly improve the irregularities in the drive currents between the output terminals of the driver chips caused due to the above-described irregularities in the element characteristic by using only a technique of optimizing the manufacturing processes.
Furthermore, since there is a limit in the number of output terminals which can be set in one semiconductor chip due to a problem of an increase in signal delay owing to an increase in wiring length or to a reduction in production yield with an increase in the number of elements in one chip, the data driver must be necessarily configured by using a plurality of the driver chips. If the semiconductor chips are different from each other, irregularities in the drive currents between the output terminals further become large, and it is very difficult to suppress irregularities in the drive currents in the same driver chip while suppressing the same between the driver chips.
As a technique to correct irregularities in the drive currents in the driver chip, there is known a technique which additionally provides a current setting resistance in accordance with an output terminal of each driver chip and individually adjusts a resistance value of the current setting resistance. In this technique, when the number of the output terminals provided to the same driver chip is increased, adjustment of each current setting resistance becomes complicated, adjustment requires a long time and cost and a resistance setting area in the circuit configuration becomes large. Therefore, it is not suitable as a technique to suppress irregularities in the drive currents between the respective output terminals.
Therefore, in order to suppress irregularities in the drive currents between the output terminals in the same driver chip while also suppressing irregularities between the driver chips, a complicated and large-scale circuit configuration must be added between the respective output terminals and between the respective driver chips. Therefore, the data driver including the driver chips and thus the apparatus scale of the display are increased, and there is a problem that a product cost is increased.
Moreover, as described above, in the display in recent years, although realization of further clearness of gradation display is demanded with realization of high definition in the display image quality, the light emitting element type display which has been currently developed has a problem that it has not reached establishment of a technique to generate an analog output signal which can realize the sufficient gradation display when generating a drive current having an analog signal component from a digital input signal which becomes display data by digital-to-analog conversion.